Chapter PowerPoint Presentation

Transcript
Chapter PowerPoint Presentation

LEARNING OBJECTIVES
•
How to use the style attribute within an HTML tag to apply an inline style.
•
How to use the <style> and </style> tag pair to define embedded style
definitions.
•
How to create an external style sheet file and use the <link> tag to include it
within an HTML file.
•
When to use inline, embedded, and external style definitions.
•
Why the word “cascading” is used in the word cascading style sheets.
INLINE STYLES
•
Developers refer to attribute settings that appear within an HTML tag as inline
styles.
•
To specify inline styles, you place the style attribute within an HTML tag and within
the style attribute, assign values to the formatting properties that you desire.
•
If you have a simple HTML page, using inline styles is fine.
•
As the number of pages in your Web site increases, the use of inline styles often
leads to redundancy of effort and pages that are hard to modify.
<h1 style=“color:red”>This text is red</h1>
SETTING A BACKGROUND IMAGE
<!DOCTYPE html>
<body style="background-image:
url('http://www.websitedevelopmentbook.com/chapter07/puppy.jpg')">
</body>
</html>
SAMPLE INLINE STYLE FOR FONTS
<!DOCTYPE html>
<body style="font-family:'Comic Sans MS'">
<h1>This is a Header</h1>
<hr/>
<p>This is sample paragraph text!</p>
</body>
</html>
POSITIONING IMAGES
<!DOCTYPE html>
<body>
<img src="http://www.websitedevelopmentbook.com/Chapter07/cigar.jpg"
style="position:absolute; left:400px; top:300px; z-index:1;" />
<img src="http://www.websitedevelopmentbook.com/Chapter07/wine.jpg"
style="position:absolute; z-index:0;" />
<img src="http://www.websitedevelopmentbook.com/Chapter07/pizza.jpg"
style="position:absolute; left:500px; top:0px; z-index:2;" />
</body>
</html>
STYLING VARIOUS ELEMENTS
<!DOCTYPE html>
<body>
<h1 style="color:red; font-family:arial;">Dogs</h1>
<p style="color:blue; font-decoration:italic; textalign:left;">Dogs are great!</p>
<img style="border:0;"
src="http://www.websitedevelopmentbook.com/chap
ter07/dogs.jpg"/>
<h1 style="color:red; font-family:arial;">Cats</h1>
<p style="color:blue; font-decoration:italic; textalign:left;">Cats are great!</p>
<img style="border:0;"
src="http://www.websitedevelopmentbook.com/chap
ter07/cats.jpg"/>
<h1 style="color:red; font-family:arial;">Horses</h1>
<p style="color:blue; font-decoration:italic; textalign:left;">Horses are great!</p>
<img style="border:0;"
src="http://www.websitedevelopmentbook.com/chap
ter07/horses.jpg"/>
</body>
</html>
EMBEDDED STYLE DEFINITIONS
•
An inline style is so named because it appears “inline” within an HTML tag. The
inline style applies only to the tag within which it appears.
•
In contrast, an embedded style, which you will define using the <style> and
</style> tag pairs, will, by default, apply to all occurrences of a tag.
•
To define an embedded style, you place the <style> and </style> tag pair inside
the <head> and </head> tag pair at the top of your file.
<head>
<style type="text/css">
h1 { color:blue; }
</style>
</head>
<body>
EMBEDDED STYLES
<!DOCTYPE html>
<head>
<style type="text/css">
h1 { color:red; font-decoration:italic; text-align:left; }
p { color:blue; font-decoration:italic; text-align:left; }
img { border:0; }
</style>
</head>
<body>
<h1>Dogs</h1>
<p>Dogs are great!</p>
<img src="http://www.websitedevelopmentbook.com/chapter07/dogs.jpg"/>
<h1>Cats</h1>
<p>Cats are great!</p>
<img src="http://www.websitedevelopmentbook.com/chapter07/cats.jpg"/>
<h1>Horses</h1>
<p>Horses are great!</p>
<img src="http://www.websitedevelopmentbook.com/chapter07/horses.jpg"/>
</body>
</html>
INLINE STYLES OVERRIDE EMBEDDED
•
When you define style properties for an HTML element using embedded styles,
you set the default format for each occurrence of the tag throughout your HTML
file.
•
After you define a default style, there may be times when you want to use a
unique format for a specific tag within your page.
•
In such cases, you can override the embedded style definition using an inline
style.
OVERRIDING A STYLE DEFINITION
<!DOCTYPE html>
<head>
<style type="text/css">
p { color:blue; background-color:orange; }
</style>
</head>
<body>
<p>11111111</p>
<p style="background-color:yellow">2222222</p>
<p>33333333</p>
</body>
</html>
EXTERNAL STYLE SHEETS
•
•
•
•
Embedded styles let you control the format of HTML elements throughout your entire
page. In this way, you can quickly apply or later change the entire look and feel of your
page.
Most Web sites, however, consist of multiple pages. Admittedly, you could place the
same embedded style definitions at the top of each page. However, do so requires
repetitive work. Further, should you later decide to change an element’s appearance,
you would again have to edit every page’s corresponding file—which is not only time
consuming, but also error prone.
An external CSS style sheet lets you place all of your CSS style definitions within one
file that you then reference from within each of your HTML page files. When a user
views a page, the browser will download and apply the style definitions provided in the
corresponding .CSS file. Should you later need to change a style, you simply edit the
.CSS file and your changes will automatically apply to the pages that use the file.
To create an external style sheet file, you use a text editor, just like you would to create
an HTML file. Within the external style sheet file, you do not use the <style> and
</style> tag pair to define your style properties.
SAMPLE EXTERNAL STYLE SHEET (SITESTYLES.CSS)
h1 { color:red; background-color:yellow; font-family:'Comic Sans MS'; }
p { color:blue; background-color:orange; font-family:Arial; }
LINKING IN THE STYLE SHEET
<head>
<link rel="stylesheet" type="text/css" href="SiteStyle.css" />
</head>
UNDERSTANDING THE “CASCADING” IN
CASCADING STYLE SHEETS
REAL WORLD: VALIDATING CSS STYLES
SUMMARY
•
Across the Web, developers make extensive use of cascading style sheets, CSS,
to format elements within a Web page.
•
By default, if a Web developer does not specify CSS attributes for an HTML
element, a browser will use its own default, built-in, formatting.
•
To specify formatting using CSS, developers can use inline styles, embedded
styles, and external styles. An inline style appears within an HTML element tag
and affects only that occurrence of the element.
•
An embedded style, in contrast, affects all of the corresponding tags within an
HTML file.
•
And finally, an external style sheet file defines styles that a developer can easily
apply to multiple pages within a Web site. Using external style sheets, the
developer can apply consistent styles throughout a site and easily and effectively
add or modify styles.